Atomic Concentration Research Articles

Effects of interstitial impurities (H, O, and He) on the structure and electronic properties of [formula omitted]–W: A density functional theory-based study

The A15 structure of W, the β–W, exhibits better properties for spintronics applications than bcc α–W. Previous works found that impurities could stabilize β–W. It is therefore important to identify the role and effects of impurities in the material. Hence, we performed DFT-based calculations and investigated the effects of interstitial impurities (12.50% and 1.56% atomic impurity concentrations of H, O, and He) on the structural and electronic properties of β–W. We also investigated α–W for comparison. We found that the binding energy of O is more favored in β–W than in α–W. However, the cohesive energy per atom of β–W is higher than α–W only when there is 12.50% atomic concentration of O in the system. This suggests that O has the tendency to induce α–W-to-β–W transition at this concentration of O. We found that the binding energies of H in β–W are energetically more favorable than in α–W, but the cohesive energies per atom are higher in α–W. These results imply that it will require a larger amount of energy to form β–W with H as an impurity. We found no stable site for He. Interaction between impurities and W atoms induces structural changes and an increase in the electron density of states at the Fermi level which highlights the effects of impurities in β–W.

Atomic scale mechanism of β to γ phase transformation in gallium oxide

We report the detailed mechanism behind the β to γ phase transformation in Sn-doped and Si-implanted Ga2O3 that we determined based on the direct observation of the atomic scale structure using scanning transmission electron microscopy (STEM). Quantitative analysis of the STEM images revealed that the high concentration of impurity atoms favored the formation of interstitial–divacancy complexes, which then leads to the secondary relaxation that creates additional interstitial atoms and cation vacancies, resulting in a local structure that closely resembles γ-Ga2O3. We explain the mechanism of how the impurity atoms facilitate the transformation, as well as the detailed sequence of the local γ phase transformation. The findings here offer an insight on how the lattice respond to the external stimuli, such as doping and strain, and transform into different structures, which is important for advancing Ga2O3 but also a variety of low symmetry crystals and oxides with multiple polymorphs.

Kinetics of substitutional Xe and self-interstitial Mo in γ U–10Mo: a molecular dynamic study

Diffusion is one among multiple reasons responsible for the micro-structural changes instigating substantial alterations in the macroscopic properties of materials. Simulating irradiation effects offers necessary insights into the production of radiation damages and their impact on different characteristics of nuclear fuels. Atomistic simulations were performed to obtain the migration energy and diffusion pre-factor of a single Xenon (Xe) substitutional as a function of percent atomic vacancies concentration in γ Uranium 10 wt% Molybdenum (γ U–10Mo). We observed a decrease and an increase in the migration energy and diffusion pre-factor respectively with an increase in the population of vacancies which proved that vacancy diffusion is a true mechanism of Xe in metals. Nudged elastic band (NEB) calculations were involved to obtain the migration energy of a self-interstitial Mo for intra- and inter-planar transitions. We observed the migration energy of Mo substantially higher than that of Xe which indicated that Xe is more mobile than Mo in bcc γ U–10Mo.

The modification of bubble characteristics and chalcopyrite surface hydrophobicity in water containing NaCl

Recycled water has been utilized in various industries as a response to global water scarcity, despite the accumulation of salts in process water and the subsequent alteration of water structures and interfacial properties caused by salts. This study investigated the effect of NaCl, a dominant salt in process water in mineral flotation plants, on chalcopyrite flotation, a major source of copper. For the first time, this study decoupled the effects of surface hydrophobicity and bubble characteristics modified by NaCl on chalcopyrite flotation and also considered the effect of NaCl on the true floatability by removing the effect of collectors and the recovery caused by mechanical entrainment. Cyclic voltammetry (CV) and Cryogenic x-ray photoelectron spectroscopy (Cryo-XPS) were combined to understand chalcopyrite surface oxidation and the formation of hydrophobic products, while bubble size distributions were measured to understand bubble characteristics. It was demonstrated that the addition of NaCl improved the true flotation of chalcopyrite slightly from de-ionised water to 0.1 M NaCl solution, but significantly from 0.1 M NaCl solution to 0.7 M and 1.2 M NaCl solutions. This trend was consistent with the extent of oxidation on the chalcopyrite surface, but inconsistent with the atomic concentration of hydrophobic oxidation products formed. It was identified that the atomic concentration of hydrophobic oxidation products on the chalcopyrite surface was optimised in 0.1 M NaCl solution, suggesting that the surface hydrophobization by NaCl was not a primary factor in chalcopyrite flotation. In contrast to the reduced amount of hydrophobic oxidation products on the chalcopyrite surface in 0.7 M and 1.2 M NaCl solutions, the bubble size was reduced significantly, suggesting that bubble size played a significant role in chalcopyrite flotation in saltwater containing NaCl.

A Stunt of Sustainability: Artificial humic substances can generate and stabilize single Fe(0) species on mineral surfaces.

Iron species are omnipresent in fertile soils and contribute to biological and geological redox processes. Here, we show by advanced electron microscopy techniques that an important, but previously not considered iron species, single atom Fe(0) stabilized on clay mineral surfaces, is contained in soils when humic substances are present. As the concentration of neutral iron atoms is highest under frost logged soil conditions, their formation can be attributed to the action of a then reductive microbiome. The Fe0/Fe2+ couple is with -0.04 Volt standard potential highly suited for natural environmental remediation and detoxification, and its occurrence can help to explain the sustained auto-detoxification of black soils.

Magnetism caused by 3d-metals

Magnetic properties of Ag2S doped with 3d-transition metals were studied using density functional theory (DFT). It was found that magnetic elements such as Co, Cr and Mn cause magnetism in the structure. The nature of this magnetism is mainly from the 3d-states of the magnetic elements. The magnetic moment of supercells containing various concentrations (x= 2.08%, 4.1%, 8.3%) of dopant atoms has been studied. It was determined that the contribution of the magnetic elements is significant in the total magnetic moment of supercells. Calculation results reveal that when doped with impurity atoms, supercells show half metallicity and ferromagnetic (FM) nature which makes them the best candidate to be used in the field of spintronics.

Periodic Arrays of Dopants in Silicon by Ultralow Energy Implantation of Phosphorus Ions through a Block Copolymer Thin Film.

In this work, block copolymer lithography and ultralow energy ion implantation are combined to obtain nanovolumes with high concentrations of phosphorus atoms periodically disposed over a macroscopic area in a p-type silicon substrate. The high dose of implanted dopants grants a local amorphization of the silicon substrate. In this condition, phosphorus is activated by solid phase epitaxial regrowth (SPER) of the implanted region with a relatively low temperature thermal treatment preventing diffusion of phosphorus atoms and preserving their spatial localization. Surface morphology of the sample (AFM, SEM), crystallinity of the silicon substrate (UV Raman), and position of the phosphorus atoms (STEM- EDX, ToF-SIMS) are monitored during the process. Electrostatic potential (KPFM) and the conductivity (C-AFM) maps of the sample surface upon dopant activation are compatible with simulated I-V characteristics, suggesting the presence of an array of not ideal but working p-n nanojunctions. The proposed approach paves the way for further investigations on the possibility to modulate the dopant distribution within a silicon substrate at the nanoscale by changing the characteristic dimension of the self-assembled BCP film.

Adsorption of radon on transition metal functionalized graphene monolayer with external effects

The noble gas radon (Rn) is radioactive and can gravely harm the human body. As a result, capturing and dealing with Rn gas is an important task, in terms of radiation protection. The large specific surface area of graphene renders it a potential candidate for gas adsorption applications. Along these lines, in this work, theoretical calculations based on the density functional theory were presented to systematically explore the adsorption properties of Rn on transition metal (TM) functionalized graphene monolayer. The adsorption energies of Rn atoms on the functional graphene were estimated up to −0.873 eV, according to our computed results. The increase in the concentration of Rn atoms and the ambient temperature led to a reduction in the adsorption energy of Rn on the surface. To effectively control the adsorption characteristics, electric field and stress were externally added. The calculation results showed that a negative electric field and proper deformation could significantly improve the adsorption of Rn to TM functionalized graphene. In this work, it was demonstrated that TM functionalized graphene could be successfully used as an adsorber of Rn atoms with promising results. In addition, the adsorption properties can be controlled and enhanced under the application of an external field, as well as a stress load, which is of great significance for application in radiation protection.

Ultrasound application in alkaline pretreatment process of spodumene to improve particle floatability

Selective surface dissolution was found to be important in spodumene flotation. In this study, we proposed to introduce ultrasound into the pretreatment process to accelerate particle vibration and cavitation, as well as the migration of mineral surface components to solution. Micro-flotation results showed that the flotation recovery of spodumene can be 86.08% by ultrasound pretreatment, but only 39.30% by traditional mechanical agitation pretreatment. Compared with traditional mechanical agitation, ultrasonic pretreatment can shorten the pretreatment process, reduce the dosage of agents, reduce the mechanical agitation speed, and improve the efficiency of the pretreating process. Inductively coupled plasma analysis showed that, in the ultrasonic system, the amount of Li, Al, and Si species in the solution was twice as much as those in the traditional preprocessing system. Moreover, the scanning electron microscope results demonstrated a larger surface dissolution area in the ultrasonic system. X-Ray photoelectron spectroscopy results showed that the atomic concentration of Si species on the spodumene surface decreased, whereas the relative atomic concentrations of Li and Al species increased, indicating that the ultrasound effect strengthened the selective dissolution of elements on the mineral surface. The high-resolution spectra of O 1s showed that more collectors are adsorbed on the mineral surface treated by ultrasonic pretreatment.

Metal particle size effects over the Ni/SAPO-11 bifunctional catalyst

The prominent size effects of metal nanoparticles (NPs) are mainly reflected in the change of electronic and geometric properties, which may induce distinct catalytic performance of the catalyst. Herein, Ni/SAPO-11 bifunctional catalysts with controllable sizes of Ni NPs were synthesized to investigate the particle size effects in n-hexane hydroisomerization. The results show that decreasing Ni particle size from 11.7 to 5.3 nm increases the concentration of surface Ni atoms and the proportion of low-coordinated Ni sites (corner, step sites) by 1.7 and 1.5 times, respectively. The low-coordinated surface Ni atoms have rich dangling bonds and high surface energy, resulting in greatly improved H2 adsorption and activation abilities. Moreover, an increased proportion of low-coordinated Ni sites within the Ni cluster shifts the d-band center upward, further enhancing the adsorption and activation of reactants. The intrinsic catalytic activity (turnover frequency) of 5.3 nm Ni NPs is ca. 2 times as much as that of the 11.7 nm ones. Besides, the smaller Ni NPs enhanced the metal–acid synergy, leading to a higher selectivity to isomers. This work provides deep insights into the metal particle size effects over the bifunctional Ni/SAPO-11 hydroisomerization catalysts and can be extended to various metal supported catalysts.

Robustness of semimetallic transport properties of TaAs against off-stoichiometric disorder

TaAs single crystals were grown by a standard chemical vapor transport method. The single-crystallinity and homogeneous distribution of elements were confirmed by transmission electron microscope and x-ray diffraction observations. Positron annihilation measurements revealed that the atomic vacancy concentration was kept below 10−5 at. %. However, inductively coupled plasma analysis showed an As-deficient (7–9 at. %) off-stoichiometry. First-principles calculations implied that the off-stoichiometry could be compensated for with excess Ta antisite defects, thereby inducing metallic states. Nevertheless, excellent semimetallic transport properties of a well-suppressed carrier density (≲1018 cm−3), ultrahigh carrier mobility (≳106 cm2/V/s), and large transverse magnetoresistance (>200000% at 9 T) with the quantum oscillation were obtained at 1.7 K. This indicated the robustness of semimetallic transport properties against the off-stoichiometric disorder and the quenching of metallic conduction associated with excess Ta atoms. The negative longitudinal magnetoresistance, which is considered evidence of a Weyl semimetal (chiral anomaly), was not observed. These data were discussed with theoretical calculations.

Tetracene crystals as promising anode material for alkali metal ion batteries

Using first-principles calculations we study the energetics of alkali metal (AM) atom intercalation into bulk tetracene crystals. We show that, contrary to the adsorption of Li and Na atoms on isolated tetracene molecules, the intercalation of these and other (K, Rb, Cs) AM atoms into bulk tetracene crystals is energetically favorable (with respect to forming an infinite AM crystal) in a wide range of AM concentrations and that the intercalation energy is noticeably lower than that for intercalation into graphite, a material used today in anodes of AM batteries. In case of Li, there is no swelling of the intercalated crystals, and for Na the increase in crystal volume is less than 10%, which makes crystalline tetracene attractive from the viewpoint of energy storage, as the capacity exceeds the theoretical capacity of graphite. We further assess diffusion barriers of AM atoms, which for Li and Na proved to be below 0.5 eV, indicating a high diffusivity of these atoms already at room temperature. We also study the effects of intercalation on the electronic properties of the system, and show that several bands can be filled upon intercalation, so that the system exhibits semiconducting–metallic–semiconducting behavior when AM atom concentration increases. Our results shed light on the perspective of using AM atom intercalation into tetracene crystals for energy storage and tuning the electronic properties of this system.

Cellulose nanocrystals doped silver nanoparticles immobilized agar gum for efficient photocatalytic degradation of malachite green

The present study involves the synthesis of green functional material based on the silver nanoparticle (Ag NPs) doped cellulose nanocrystals (CNC) immobilized agar gum (AA) biopolymer using chemical coprecipitation method. The stabilization of Ag NPs in cellulose matrix and functionalization of the synthesized material through agar gum was analyzed using various spectroscopic techniques such as Fourier Transform Infrared (FTIR), Scanning electron microscope (SEM), Energy X-Ray diffraction (EDX), Photoelectron X-ray (XPS), Transmission electron microscope (TEM), Selected area energy diffraction (SAED) and ultraviolet visible (UV–Vis) spectroscopy. The XRD results suggested that the synthesized AA-CNC@Ag BNC material is composed of 47 % crystalline and 53 % amorphous nature having distorted hexagonal structure due to capping of Ag NPs by amorphous biopolymer matrix. The Debye-Scherer crystallite sized was calculated as 18 nm which is found in close agreement with TEM analysis (19 nm). The SAED yellow fringes simulates the miller indices values with XRD patterns and supported the surface functionalization of Ag NPs by biopolymer blend of AA-CNC. The XPS data supported the presence of Ag0 as indexed by Ag3d orbital corresponding to Ag3d3/2 at 372.6 eV and Ag3d5/2 at 366.6 eV. The surface morphological results revealed a flaky surface of the resultant material having well distributed Ag NPs in the matrix. The EDX and atomic concentration results given by XPS supported the presence if C, O and Ag in the bionanocomposite material. The UV–Vis results suggested that the material is both UV and visible light active having multiple SPR effects with anisotropy. The material was explored as a photocatalyst for remediation of wastewater contaminated by malachite green (MG) using advance oxidation process (AOP). Photocatalytic experiments were performed in order to optimize various reaction parameters such as irradiation time, pH, catalyst dose and MG concentration. The obtained results showed that almost 98.85 % of MG was degraded by using 20 mg of catalyst at pH 9 for 60 min of irradiation. The trapping experiments revealed that •O2− radicals played primary role in MG degradation. This study will provide new possible strategies for the remediation of wastewater contaminated by MG.

Ppb-level butanone sensor based on porous spherical ZnCo2O4/ZnO through the synergy effects of Co2+ atoms and unique wrinkled structure

Transition metal (TM) elements are often applied through doping to improve sensor performance for the detection of toxic and hazardous gases. Elemental valence conversion plays an important role for gas electron transfer and vacancy oxygen formation in the sensing process. However, relevant studies are rarely reported. In this work, uniformly dispersed porous spherical hollow ZnCo2O4/ZnO with wrinkled surfaces is prepared via a simple hot solvent method and used to investigate the role of valence conversion in gas sensing. ZnCo2O4/ZnO-2 has a response 844.5–100 ppm butanone with 79.25 % Co2+ atoms concentration, 7.7 times higher than ZnO. The material shows a good linearity for 0.1–100 ppm butanone with a lower detection limit 0.01 ppm. The research reveals that the superior performance of the sensor attributes to the synergy effects of Co elements doping, ZnCo2O4 modification and unique wrinkled structure. The effect of Co valence state in ZnO and ZnCo2O4 is analyzed by XPS combined with DFT on gas sensitization.

Large Annular Dipoles Bounded between Single‐Atom Co and Co Cluster for Clarifying Electromagnetic Wave Absorbing Mechanism

AbstractIt is very challenging to demonstrate the intrinsic feature and absorption mechanism for electromagnetic (EM) wave absorber since dipole polarization loss is always discussed together with magnetic loss, conductive loss, defects/interfacial polarization, and so on. To address this issue, here, a kind of atomic composites is reported, including single‐atom Co and Co cluster with controllable atom dipole to tune the polarization and establish the link between dipole polarization and the EM wave absorption. Using a chemical synthesis route, the atomic composites are fabricated, including Co single‐atom (SA) sites and cluster (Cs) on nitrogen‐doped graphitic carbon (Co1+Cs/NGC). Due to the special design, the effect of magnetic loss, conductive loss, and interfacial polarization on EM wave dissipation can be ignored so that it can only highlight dielectric loss caused by dipole polarization. And, by controlling the Co atoms concentration, it can tune the valence state of Co atoms between 0 to +2 to control dipole polarization and relaxation. As a result, the Co1+Cs/NGC‐2 with Co concentration of 6.0 wt% exhibits optimized dipole moments and thus excellent absorption performance (the reflection loss exceeds −54.3 dB, and the effective absorption bandwidth with RL ≤−10 dB reaches 7.0 GHz at 2.0 mm) due to the effective dipole polarization caused by the large annular dipole bounded between Co SA sites and Co Cs. This study proposes a simplified model to clarify EM wave absorption mechanism from atom view.

Potassium Poisoning Effects on Sol‐gel Mn/TiO2Catalyst for Selective Catalytic Reduction (SCR) of NOx with NH3at Low Temperature

AbstractMn/TiO2catalysts exhibited more excellent activity and higher selectivity in low‐temperature SCR of NOx with NH3. Alkali metal, particularly potassium presented in the ash, could severely deactivate SCR catalyst and then reduce its lifetime. In this study, sol‐gel Mn/TiO2catalyst was employed to evaluate its SCR activity with and without the presence of KNO3at 100–300 °C. The influence of various parameters such as KNO3loading amount, calcination time, temperature and catalyst deactivation was investigated. The characterization results indicated that the doping of potassium on Mn/TiO2surface obviously resulted in a great decrease of reducibility, surface acidity and NH3adsorption capacity. XPS spectra revealed the decrease of Mn4+atomic concentration and chemisorbed oxygen species caused by potassium doping. In addition, obvious variation of potassium states (K1.04Ti8O16) was detected for K−Mn/TiO2catalyst after calcining treatment, which may lead to a poorer performance of SCR catalyst.

Increasing the Efficiency of Silicon Solar Elements by Doping with Nickel

It is shown that in the near-surface region of the solar cells (SCs) the concentration of nickel atoms is higher than in the bulk by 2–3 orders of magnitude, therefore, the gettering rate in the near-surface region is higher. Optimal modes of gettering by nickel clusters (i.e., nickel diffusion – Т = 800–850 °С, additional thermal annealing – Т = 750–800 °С) and the structure of a silicon SC were experimentally determined, which makes it possible to increase the efficiency of silicon SCs by 25–30% relative to the control. The physical mechanisms of the influence of the processes of diffusion of impurity nickel atoms and additional thermal annealing on the state of nickel atoms in the near-surface region and the SCs base and, accordingly, on the parameters of the SC are revealed. Physical models of the structure of a cluster of nickel atoms in silicon and the process of fast diffusing impurities gettering by clusters of nickel atoms are created. The binding energy of fast dissusing impurities atoms with a nickel cluster is estimated to be ~ 1.39 eV. The calculation shows that doping with nickel can increase the lifetime of minority charge carriers by 2–4 times, and the collection coefficient by 1.4–2 times. The experiment showed an increase in the minority charge carriers lifetime up to 2 times and an increase in efficiency by 25–30%.

Room temperature ferromagnetism of a crystalline semiconductor compound Hg<sub>1 – <i>x</i></sub>Fe<sub><i>x</i></sub>Se at extremely low concentration of impurity iron atoms (<i>x</i> ≤ 0.06 at %)

On the single crystals of Hg1 – xFexSe (х ≤ 0.06 at %) with an extremely low concentration of the impurity iron atoms at room temperature (T = 300 K), high-temperature ferromagnetism of a new type in a impurity donor electron system was experimentally discovered.

Ti2Ni and TiNi3 intermetallic compounds to prepare dense TiNi alloy with enhanced recovery property

TiNi alloys fabricated through powder metallurgy suffer from low density and unsatisfactory recovery strain. In this paper, Ti2Ni/TiNi3 intermetallic compounds instead of Ti/Ni elements powders were chosen to improve both the relative density and recovery strain of TiNi alloy. The Kirkendall pores can be avoided due to the decreasing of the Ni atomic chemical concentration gradient in Ti2Ni/TiNi3, and the cracks and pores can be filled by liquid Ti2Ni, which improves the density of TiNi alloy up to 96.8%. Benefiting from the nano-crystalline/ amorphous matrix, the recoverable strain of TiNi alloy increased up to 7.46%. This novelty method shows great potential in developing low-cost and high-performance TiNi shape memory alloy.

Interactions between displacement cascades and grain boundaries in NiFe single-phase concentrated solid solution alloys

Single-phase concentrated solid solution alloys (SP-CSAs) are promising structural materials with excellent irradiation resistance. It is very important for their application in nuclear reactor structures to understand the interactions between their grain boundaries (GBs) and irradiation-induced defects. With molecular dynamics (MD) simulations, the displacement cascades in NiFe SP-CSAs with Σ5(210) symmetrical tilt GB were studied. Compared with pure Ni, NiFe has higher sink strength of GB for vacancies but has little effect on the interstitial absorption of GB. The formation energies of interstitials and vacancies near the GB are more dispersed, so that the point defects are more difficult to aggregate, which is beneficial for the recombination of interstitials and vacancies near the GB. Both the formation energies of point defects and the sink strengths of GB for point defects could be changed with the SP-CSA compositions. When the Fe atom concentration is higher than 30 at.%, the point defects are easier to annihilate. Both the effects of the PKA energy and the PKA-GB distance on the displacement cascades damage can be explained with the size of overlapping region between the cascade region and GB. In addition, the formation of SP-CSAs helps to annihilate the vacancies in NiFe with Σ37(750) symmetrical tilt GB and Σ5 twist GB.